Skip to main content

Full text of "Special scientific report:"

See other formats


o 



=> * 



t!5z$y w 




CD 

> |S| 
co — co — co i co 

shiiws ssiavaan libraries Smithsonian institution NoiiniusNi nvinoshiiws S3iava 

CO Z CO Z . CO Z CO 

< 2 /$m^ < .«. 2 -J^ < ^-^T7^ 2 




z 



H%c5 

- CO 




x 
i- 






I' z ^^^ 00 
IONIAN INSTITUTION NOIinillSNI NVINOSHIIWS S3iavaail LIBRARIES^SMITHSONIAN INSTITU" 
oo 5 \ °° _ _ 5 co - 

OS /*£? ^o\ _ 

< 
cc 

jhiiws ssiavaan^LiBRARiEs Smithsonian institution NouniiiSNi^NviNOSHiiws S3iava 

\ Z CO ± CO — CO 

JON IAN INSTITUTION NOIinillSNI NVINOSHIIWS S3iavaan LIBRARIES SMITHSONIAN INSTITU' 

O 

%# I 
co * z w z €/>"..*= co 

jhiiws S3 1 a va an libraries Smithsonian institution nohdiiisni nvinoshiiws ssiavb 

co ~ co 5 _^ co — co 

O < 

^ 2 ^^ 5 ^P 7 2 '*W 5 "^^ 2 ^P 7 s ^ 2 ^% 



cz 

30NIAN~INSTITUTI0N NOIini!lSNl" J NVINOSHllWS S3iavaai1 LIBRARIES SMITHSONIAN INSTITU' 
r- z r- . z i- Z <~ 








SHIIWS S3iavaan~LIBRARIES SMITHSONIAN _ INSTITUTION a, NOIinillSNI~NVINOSHllWS S3iava 
co z •, co z . co z w 

30NIAN INSTITUTION ^NOIinillSNI NIVINOSHIIMS^SS I a Va a 11 LI B RAR I ES^SMITHSONIAN INSTITU" 

00 5 > 00 — 00 





H /£tf^V S 4& " J 




jhiiws ssiavaan^LiBRARiEs Smithsonian institution NouniiiSNi'WiNOSHiiws S3iav^j 




co = CO E CO 

SON IAN INSTITUTION NOIinillSNI NVIN0SH1IWS S3iavaan LIBRARIES SMITHSONIAN INSTITU 

Z ,vy ' W Z ^_^ CO Z ..... CO Z 






jfe 



-./ 



*.<% v^\n i /sS; 



V, 



% 



co 



co — co ± en — to 

iARIES SMITHSONIAN INSTITUTION NOIinillSNI NVINOSH1IWS S3iavaan LIBRARIES SMITHS 
z » co z co z •„ co 

# l^^ 7 | %T |,^^ |^%#/ ^^ I 

nillSNI NVINOSHilWS W S3 I a Va 3 n\| B RAR I ES^SMITHSONIAN^INSTITUTION NOIinillSNI_NVINOS 

Z CO 

Co ><^>a ,v?>v ^ 






CO 



\ 



O 

SMITHSONIAN INSTITUTION NOIinillSNI~'NVINOSHiMS :Z S3 I HVd 8 H LI B RAR I ES SMITHS 




nillSNI NVINOSH1IIAIS S3iavaan LIBRARIES SMITHSONIAN~INSTITUTION NOIinillSNI NVINOS 
to Z ... co z co z 





?|x ^ 







?ARIES W SMITHSONIAN INSTITUTION NOIinillSNI NVINOSHIIWS^SS I H Va 8 11 LI B RAR I ES^SMITHS 

CO ^ CO — (/) — CO 

3) < 
K 

_I Z _J Z *■ _l z 

niusNi_NviNOSHims_S3iavyan libraries Smithsonian institution NoiinniSNi nvinos 

*%l %L^lf^i/^%J 0^-1 0%\^ i^%\l \ 

- V^. ' CO X^f^/ - X^IP^ W * ' ' ' ~ VgggSg/ CO ^j^/ ^ >^ 

co _ co r: co iE co 

IARIES SMITHSONIAN INSTITUTION NOIinillSNI NVIN0SH1IWS S3iavaan LIBRARIES SMITHS 
^ z. co z to z , to 

^I_NVIN0SH1IWS W S3 I d Vd a llf LI B RAR I ES^SMITHSONIAN JNSTITUTION ^NOIinillSNI NVINOS 




en 




CO 



V : . 



z -J Z _| Z _i z 

lARIES_SMITHSONIAN_INSTITUTION NOIinillSNI NVINOSH1IWS S3iavaail LI B RAR I ES SMITHS 

CD 

> 

— to ± — co 

.niusNi nvinoshiiws S3iavaan libraries Smithsonian institution NoiiniusNi nvinos 

Z CO Z.i-.CO Zvv-tO z 





U.S. DEPARTMENT OF COMMeIISS 1 } 



vssm 



NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

NATIONAL MARINE FISHERIES SERVICE 



,,d Biology of the 
Fresh-Water Shrimp, Macrobrachium, in the 
Lower St. Paul River, Liberia, 1952-53 




SPECIAL SCIENTIFIC REPORT-FISHERIES Na 626 



NOTE 

Until October 2, 1970, the National Marine 
Fisheries Service, Department of Commerce, 
was the Bureau of Commercial Fisheries, De- 
partment of the Interior. 



UNITED STATES DEPARTMENT OF COMMERCE 

Maurice H. Stans, Secretary 

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

NATIONAL MARINE FISHERIES SERVICE 
Philip M. Roedel, Director 



Commercial Fishery and Biology of the 

Fresh-Water Shrimp, Macrobrachium, in the 

Lower St. Paul River, Liberia, 1952-53 



By 
GEORGE C. MILLER 



Contribution No. 141, National Marine Fisheries Service Tropical 
Atlantic Biological Laboratory, Miami, Fla. 33149 



Special Scientific Report — Fisheries No. 626 



Washington, D.C. 
February 1971 



CONTENTS 

Page 

Introduction 1 

Methods and measurements 2 

Commercial fishery 2 

Location 2 

Description of the fishery 2 

Economic value 4 

Biology of M. vollenhovenii 5 

Distribution 6 

Description 6 

Length-frequency distributions 6 

Weight-length relation 9 

Fecundity and spawning 9 

Disease 11 

Biology of M. macrobrachion 11 

Description 11 

Species and size composition of culls from the commercial catch 12 

Acknowledgments 12 

Literature cited 13 



in 



Commercial Fishery and Biology of the Fresh-Water Shrimp, 
Macrobrachium, in the Lower St. Paul River, Liberia, 1952-53 



By 

GEORGE C. MILLER, Zoologist 1 

National Marine Fisheries Service 

Tropical Atlantic Biological Laboratory 

Miami, Florida 33149 



ABSTRACT 

A small fishery was conducted for the large commercial fresh-water shrimp, Macrobrach- 
ium vollenhovenii, using traps. A second smaller species, M. macrobrachion, was culled from 
the trap catch for the fishermen's use. The estuarine fishery was seasonal (May to Janu- 
ary) , during the period of low salinity. Cost of raw tail meats to the consumer was over 
$1.00 (U.S.) per pound. The fishermen derived more than $7,500 from the fishery. 

Commercial shrimp, M. vollenhovenii, spawned in the estuary from May to January. 
Fecundity was estimated at 12,000 to 45,000 eggs per female. As the embryo developed 
the color of the egg changed from red to brown. Embryonic and larval development to 
time of setting of M. vollenhovenii was believed similar to that of M. rosenbergii, 50 to 
65 days. An intensive push-net fishery was conducted by women on the zero age group soon 
after the juveniles had set. Juvenile shrimp were not caught by traps. Monthly length dis- 
tributions indicated that the fishery was supported by age group one, which was replaced 
at the end of the season by age group zero. Age group zero grew rapidly and reached a 
modal length of 75 to 80 mm. in 9 months in January; and adults grew slowly and increased 
in length to 85 to 90 mm. in May, and 100 to 105 mm. in November. The weight-length re- 
lation of M . vollenhovenii ovigerous females was expressed by the equation Log W = — 4.656603 
+ 3.011392 Log L, and males and nonovigerous females by Log W = — 4.829560 + 
3.092213 Log L. 

The characters used to distinguish M. macrobrachion from the commercial shrimp are 
given. The smaller species (modal length 50 to 54 mm.), constituted 88 percent of the 
shrimp discarded from the commercial catch. The trap fishery harvested the adults of the 
two species, which differed considerably in length, without harm to either species. 



INTRODUCTION 

Fresh-water shrimp, Macrobrachium (fam- 
ily Palaemonidae) , are found worldwide in 
tropical fresh and brackish waters. Commer- 
cial fisheries exist for many of the species 
(Holthuis and Rosa, 1965). Interest has been 
shown in the possibility of using fresh-water 



1 The author made this study while on loan from the 
U.S. Fish and Wildlife Service to the U.S. Foreign 
Operations Administration, as Technical Advisor in 
Marine Fisheries to the Liberian Government. 



shrimp for aquaculture because of their fast 
growth rate (Dobkin, 1967; Ling, 1967a, 
1967b; Ling and Merican 1962; and William- 
son, 1967). Publications on the fresh-water 
shrimp indigenous to West Africa consist pri- 
marily of systematic studies. 

A seasonal commercial fishery exists for 
fresh-water shrimp (known locally as craw- 
fish), in the lower St. Paul River near Mon- 
rovia, Liberia, West Africa (fig. 1). In 1952- 
53, I made a general survey of the fishery and 




Figure 1. — Distribution and some geographical loca- 
tions of the commercial shrimp, M. vollenhovenii, in 
Africa. 



a study of the biology of the commercial spe- 
cies. Because my primary responsibility in 
Liberia was as the Adviser in Marine Fisheries, 
my study was a secondary project limited by 
a lack of time. 

The commercial catch in the lower St. Paul 
River is composed of two species: Maero- 
brachium vollenhovenii (Herklots), a large 
commercial shrimp; and Macrobrachium ma- 
crobrachion (Herklots), a small shrimp culled 
from the catch and eaten by the fishermen. 
Both species are of commercial importance in 
Dahomey (Monod, 1966). The present report 
is concerned primarily with the large commer- 
cial fresh-water shrimp, M. vollenhovenii. 

METHODS AND MEASUREMENTS 

I obtained samples from the commercial 
fishery at least once a month during the season. 
Traps used, were tightly woven, and prevented 
the escapement of small shrimp. The tiny 
shrimp of the incoming year class were ob- 
tained from fishermen who collected them in 
burlap push-nets. Total length, from the base 
of the eyestalk to the tip of the telson, was 
measured to the nearest millimeter with a 
simple measuring board (Pruter and Harry, 
1952). Shrimp were weighed on a Harvard 



Trip Balance after the major chelipeds had 
been removed. Specimens 60 mm. long or 
longer were weighed to the nearest gram ; those 
less than 60 mm. were weighed to the nearest 
0.1 g. Salinity samples were taken at stations 
in the estuaries within 1.6 km. (1 mile) of the 
mouths of the Mesurado and St. Paul Rivers. 

COMMERCIAL FISHERY 

The commercial fishery for fresh-water 
shrimp is insignificant compared with the 
catch and value of other fisheries, but it is 
significant to the economy of the people of the 
lower St. Paul River. The fishery for fresh- 
water shrimp in the lower St. Paul River will 
be described and the economic value of the 
fishery estimated. 

Location 

In Monrovia, fresh-water shrimp sold were 
captured within 3.2 km. (2 miles) upstream 
from the mouth of the St. Paul River. (The 
headwaters of the St. Paul River rise in the 
highlands of Guinea, north of Liberia.) The 
shoreline, composed of rock-gravel substrate, 
varied from gradual to steep. Outcrops of 
large rocks were present along the shore and 
in the channel (fig. 2). Fishing was carried 
out within the tidal zone. 

Description of the Fishery 

Traps used in the fishery were made of 6 
to 13 mm. (14-V2 in.) wide strips peeled from 
the hard outer layer of a palm frond stem. The 
strips were tightly interlaced into a fusiform 
trap, 101 to 152 mm. (4-6 in.) in diameter 
at the large end and 457 mm. (18 in.) long 
(fig. 3). The wide end of the trap had an 
involuted opening 38 to 51 mm. (11/2-2 in.) in 
diameter, followed (within the trap) by a sec- 
ond fyke opening of the same size. 

The bait most commonly used was the white 
core of the cassava root, Manihot utilissima. 
Three or four 19-mm. (%-in.) square pieces 
were placed in each trap. When the tide was 
low, the traps were placed in the intertidal 
area and partially covered by large rocks; the 
catch (up to 36 large shrimp per trap) was 
removed on the next low tide (fig. 4) . Shrimp 
were sorted by removing the small ones for 




Figure 2. — Liberian woman lifting traps placed near rock outcrop by fishermen lower St. Paul River, Liberia, 

downstream from the William V. S. Tubman bridge. 



the fisherman's consumption and either selling 
the large ones immediately or holding them for 
the customary Saturday market. When shrimp 
were kept in holding traps in the river, the 
large chelipeds were removed to prevent can- 
nibalism. At the peak of the season, a fish- 
erman's catch was often as high as 120 dozen 
large shrimp per week. 

The fishermen's catch depended upon the 
stage of the river. During periods of heavy 
precipitation, the river flooded and the fish- 
ermen were unable to retrieve their traps. 

In the lower St. Paul River the fishery was 
directly correlated with the rainy season, May 
to November (Orton, 1954) and the runoff lag 
of the river to January (table 1). The estu- 
arine water during the rainy season was turbid 



and fresh. During the dry season, February 
to May, the estuarine water was clear, highly 
saline, and the shrimp fishery was nonexistent. 



Table 1. — Comparison of salinities (parts per thou- 
sand) in the lower St. Paul and Mesurado Rivers, 
Liberia estuaries, November-December 1953 



Date 
1953 



St. Paul River 



Mesurado River 





P.p. t. 


P.p.t. 


Nov. 2 


0.0 


18.0 


Nov. 9 


0.7 


9.2 


Nov. 16 


0.8 


16.3 


Nov. 23 


0.5 


31.0 


Nov. 30 


0.9 


20.0 


Dec. 7 


1.8 


34.4 


Dec. 14 


1.2 


23.0 




Figure 3. — Construction of fresh-water shrimp traps in the lower St. Paul River, Liberia. 



The small, mangrove-type Mesurado River, 
which adjoins the St. Paul River, lacks the 
runoff lag and becomes highly saline several 
months before the St. Paul River (table 1). 
The higher salinities and lack of rock bottom 
habitat are believed to be the primary reasons 
for the negligible numbers of fresh-water 
shrimp caught in the Mesurado River estuary. 

The oceanic waters of the Monrovia Free- 
port were directly influenced by the low sa- 
linity runoffs of the St. Paul and Mesurado 
Rivers. The Monrovia Freeport is located in- 
termediate, and a short distance between the 
two rivers. The runoff lag of the St. Paul 
River as it decreased in December-January 
was reflected by increased salinities in the 
Freeport (table 2). 



Economic Value 

The economic value of the shrimp varied 
with size. At the beginning and end of the 
season, when shrimp were small, 18 shrimp 
retailed for 25 cents (U.S.) to the consumer. 
During the rest of the season, the fishermen 

Table 2. — Salinities in the Monrovia Freeport, Liberia, 
August 1953-January 1954 



Month 



Lowest 
salinity 



Highest 
salinity 



Average 
salinity 





P.p.t. 


P.p.t. 


P.p.t. 


Aug. 


11.0 


24.0 


17.1 


Sep. 


6.2 


24.4 


12.7 


Oct. 


5.2 


23.5 


13.7 


Nov. 


18.2 


30.4 


25.2 


Dec. 


23.8 


32.8 


30.0 


Jan. 


28.8 


33.3 


31.5 







•••-« 




Figure 4. Liberian woman tending shrimp traps set in the tidal zone on a rock-gravel substratum in the 

lower St. Paul River, Liberia. 



received 25 cents per dozen. The number of 
whole shrimp per pound varied from 17 to 37 
(table 3). The tail (abdomen) weight ac- 
counted for 51 to 53 percent of the body weight, 
and the recovery of cooked and shucked tail 
meat was 21 percent of the body weight. The 
cost per pound of whole shrimp when pur- 
chased by the dozen varied from 55 to 64 cents. 
The price of shucked, cooked tail meats to the 
consumer, at 25 cents per dozen live shrimp, 
varied from $2.63 to $3.01 per pound in June. 
The value of the shrimp fishery in the lower 
St. Paul River was estimated. I was not able 
to gather total catch statistics because of the 
erratic method of marketing and the varying 
number of fishermen and traps fished. In 



July 1952, 12 fishermen were known to be 
shrimp fishing in the lower St. Paul; conserva- 
tive estimates were that 16 additional fisher- 
men participated. The entire catch by 4 fish- 
ermen in July was 481 dozen shrimp, worth 
$120.25. If their catches can be considered 
average, the estimated catch in July by the 28 
fishermen was 3,367 dozen, worth $841.75. Be- 
cause I considered July to be an average month, 
the value of the fishery during the 9-month 
fishing season probably exceeded $7,500. 

BIOLOGY OF M. vollenhovenii 

The biology M. vollenhovenii includes the 
distribution, description, length-frequency 



Table 3. — Total weights and weights of head (cephalothorax) and tail (abdomen) of M. vollenhovenii caught 
commercially in the lower St. Paul River, Liberia, June to December 1953 



Date 
1953 



Shrimp 



Body 

weight 



Head 



Weight 



% total 
body weight 



Tail 



Weight 



% total 
body weight 



Average 

weight of 

shrimp 



Shrimp 
per lb. 





No. 


G. 


G. 


% 


G. 


% 


G. 


No. 


June 13 


341 


4,180 


2,017 


48.25 


2,163 


51.75 


12.26 


37.00 


June 20 


499 


8,414 


4,101 


48.74 


4,313 


51.26 


16.86 


26.90 


Aug. 28 


86 


1,662 


813 


48.92 


849 


51.08 


19.33 


23.47 


Sept. 4 


59 


1,411 


694 


49.18 


717 


50.82 


23.92 


18.96 


Sept. 11 


50 


877 


411 


46.86 


466 


53.14 


17.54 


25.86 


Oct. 2 


33 








__. 


__ 


__ 


12.79 


35.47 


Oct. 16 


167 











__ 


__ 


22.91 


19.80 


Nov. 13 


360 








__ 


__ 





26.46 


17.14 


Nov. 27 


708 


__ 








__ 


__ 


24.99 


18.15 


Dec. 4 


874 


-- 


— 


— 


— 


— 


20.96 


21.64 



distributions of the catch, weight-length re- 
lation, fecundity and spawning, and disease. 

Distribution 

M. vollenhovenii was described by Herklots 
(1857) from specimens collected by H. Pel in 
"CSte de Guine'e." Holthuis (1951) believed 
that the type locality was erroneous because 
Pel had collected only in the Gold Coast (now 
Ghana) . Holthuis listed the synonymy of M. 
vollenhovenii and gave its distribution as the 
offshore islands of Cape Verde, Fernando Po, 
and Sao Thome', and from Senegal south along 
the West African coast to the Kunene River 
in southern Angola. 

Description 

M. vollenhovenii grows to a total length of 
more than 150 mm. In life the body is gray 
or brown with a blue lateral line on the ab- 
domen; a blue lateral line extends from mid- 
way on the carapace forward and bifurcates 
with a ventral branch to the hepatic spine and 
dorsal branch over the orbit to the tip of the 
rostrum. The rostrum is short, deep, and 
slightly upturned at the tip; the dorsal surface 
bears 11 to 15 spines and the ventral surface 
3 to 8; though the spines may or may not ex- 
tend to the tip of the rostrum, each spine is 
preceded by setae — in many specimens setae 
are found near the anterior end of the rostrum 
where no spines are present. The carpus of 
the major chela is always shorter than the palm, 
and the fingers are not pubescent. In early 



stages of development the external eggs of the 
female are orange to red, but change to brown 
in the advanced stage before hatching. 

Rostral spine counts have been used to dis- 
tinguish species of Macrobrachium. To de- 
termine variation in numbers of rostral spines, 
I made counts from 218 specimens of M. vol- 
lenhovenii taken from the lower St. Paul River 
on October 9, October 13, and November 13, 
1953. I then compared the rostral spine counts 
of shrimp from the St. Paul River, Liberia, 
with those given by Man (1904) of shrimp 
from the Catumbella River, Angola, to discover 
whether the populations differed between the 
two widely separated areas (table 4). 

The number of dorsal rostral spines on M. 
vollenhovenii ranged from 11 to 15, with one 
exception (18) given by Man (1904). Modally 
the St. Paul River shrimp had 13 dorsal rostral 
spines and Catumbella River specimens had 12. 
The small difference in counts was probably 
caused by a difference in the sizes of specimens 
(my specimens were larger than Man's) rather 
than a genetic or clinical difference between the 
two populations of M. vollenhovenii. Ventral 
rostral spines varied from three to eight, but 
both populations had four modally. 

Length-Frequency Distribution 

The commercial fishery was sampled for 
length distributions of the catch from July to 
January (1952 season) and from May to No- 
vember (1953 season). Figure 5 shows the 
length distributions of 7,648 commercial shrimp 



Table 4. — Comparison of rostral spine counts of M. 
vollenhovenii from the lower St. Paul River, Liberia, 
and the Catumbella River, Angola 



Number of 
spines 


St. Paul River 


Catumbella River 
(from Man, 1904) 


Shrimp 


% of 

total 

examined 


Shrimp 


% of 

total 

examined 




No. 


Percent 


No. 


Percent 


Dorsal-ventrJ 
11-3 


il: 
2 


0.9 





0.0 


12-3 


23 


10.6 


11 


25.0 


13-3 


11 


5.1 


2 


4.5 


14-3 


3 


1.4 


1 


2.3 


11-4 


4 


1.8 


1 


2.3 


12-4 


41 


18.8 


12 


27.3 


13-4 


61 


28.0 


7 


15.9 


14-4 


30 


13.8 


5 


11.4 


15-4 


3 


1.4 


1 


2.3 


12-5 


4 


1.8 





0.0 


13-5 


10 


4.6 


1 


2.3 


14-5 


16 


7.3 





0.0 


15-5 


6 


2.8 





0.0 



18-5 



0.0 



0.0 



2.3 



12-6 


1 


0.5 


1 


2.3 


13-6 





0.0 





0.0 


14-6 





0.0 


1 


2.3 


15-6 


1 


0.5 





0.0 


13-7 


1 


0.5 





0.0 


13-8 


1 


0.5 





0.0 


sal: 

11 


6 


2.8 


1 


2.3 


12 


69 


31.7 


24 


54.5 


13 


84 


38.5 


10 


22.7 


14 


49 


22.5 


7 


15.9 


15 


10 


4.6 


1 


2.3 



2.3 





o 
o 


39 




17.9 




14 


31.8 




4 


139 




63.8 




26 


59.1 




5 


36 




16.5 




2 


4.5 




6 


2 




0.9 




2 


4.5 




7 


1 




0.5 







0.0 




8 


1 




0.5 







0.0 


I 


sampk 


;d in 


the 


1952 


and 


1953 


seasons, 



grouped monthly in 5-mm. intervals. 

The trap catch was selective: few juveniles 
were caught before they reached the minimum 
size of maturity (45-50 mm.) . Trap selectivity 



was possibly due to a dietary difference be- 
tween the juveniles and adults. I found a sim- 
ilar selectivity in the trap catch for the western 
North American fresh-water crawfish, Pacif- 
astacus leniusculus (Dana) (Miller, 1960). 

Knowledge of the shrimps' biology and the 
length distributions of the catch led me to 
speculate that the commercial fishery was sup- 
ported primarily by a single age group. Fe- 
male shrimp with eggs in advanced stage of 
development were found from May to January, 
which would explain the wide range of the 
length distributions (fig. 5). 

The modal length increased each month 
through November during the commercial 
seasons (May to January) of 1952 and 1953. 
In the 1952 season, the modal length declined 
in December and January (no data for these 
months in the 1953 season). This type of dis- 
tribution indicates that the fishery was sup- 
ported by a single age group, which was re- 
placed late in the season by the incoming zero 
age group. Growth rate was rapid, and age 
group zero reached a modal length of 75 to 
80 mm. in 9 months. Growth of the mature 
shrimp was slow — the shrimp reached a 
modal length of 75 to 80 mm. in January, 
85 to 90 mm. in May, and 100 to 105 mm. in 
November. 

The rapid growth of juveniles, and slow 
growth of adults given for M. vollenhovenii is 
similar to the growth rate of M. rosenbergii 
reported by Ling (1967a). The females and 
males of M. rosenbergii reached a length of 
140 mm. in 5^4 months, and the females grew 
only slightly beyond 150 mm.; the male growth, 
however, continued to 200 mm. 

Two other possible explanations for the 
length distributions were examined and then 
rejected: (1) the unimodal distribution con- 
sisted of more than two age groups, the same 
as other trap caught crustaceans; and (2) the 
large shrimp, being less salinity tolerant than 
small shrimp, were the last to enter the estuary 
at the beginning of the season and the first 
to leave the estuary at the end of the season. 

The first explanation was rejected because 
the modal length increased each month. I 
found in trap-caught western North American 
fresh-water crawfish, Pacifastacus Bott, that 
aging by length distributions was nearly 



COMMERCIAL SEASONS 



1952 



1953 




20 40 60 80 100 120 140 160 



20 40 60 80 100 120 140 160 



TOTAL LENGTH (MM.) 

Figure 5. — Monthly length distributions of commercially caught shrimp, M. vollenhovenii, from the lower 

St. Paul River, Liberia. 



impossible because of overlapping age groups 
(Miller, 1960). Length distributions of the 
western crawfish plotted by month was nearly 
identical because: recruitment in each size 
interval was relatively proportionate following 
a molt; there was little variance in growth in- 
crement of the same length crawfish; there 
was no identifiable modal length increase by 
month ; and growth in the adults was a func- 
tion of food availability, not age. 



The second explanation was rejected because 
I could see no evidence in the length distribu- 
tions to support the entrance of the large adults 
into the fishery in early summer (fig. 5). If 
age group one does not die off naturally in 
December but migrates upstream or into ad- 
jacent swampy areas, then I speculate that 
these shrimp, as age group two, survivors con- 
tribute very little to the population. 



Weight-Length Relation 

The shrimp were separated into two cate- 
gories — (1) ovigerous females and (2) males 
and nonovigerous females combined. I had 
insufficient time to determine the sex of the 
nonegg bearing shrimp. Live shrimp (major 
chelae removed) were measured and weighed. 
I made no attempt to find the effect of the 
holding period on weight — any effect probably 
was insignificant, since the shrimp were fed 
by their keepers, and holding did not diminish 
the shrimps' voracious cannibalistic appetite. 

If fewer than 100 shrimp were weighed and 
measured in any monthly sample, I used the 
entire sample in my calculations; if more than 
100 were weighed and measured, only 100 were 
used. The weight-length relation of 100 shrimp 
was derived from the 15 shortest, the 15 long- 
est, and 70 shrimp taken at random from the 
sample. The weight-length relation is de- 
scribed by the equation Log W = Log a + b 
Log L, which is the logarithmic transformation 
of W = aLb, where W = weight in grams and 
L = body length in millimeters. 

The weight-length relations by month (table 
5) were plotted on logarithmic paper, but dif- 
ferences were small. Samples were then 
grouped to derive the relation between weights 



Table 5. — Weight-length relation of M. vollenhovenii 
caught in Liberia, 1952-53 



Date 


Shrimp 
examined 


b 


Log a ( — ) 




No. 






Males and 








nonovigerous 








females : 








December 1952 


100 


3.233760 


5.104878 


January 1953 


69 


3.103854 


4.900119 


February, Marc 


M 






and April 19c 


35 






May 1953 .... 


100 


2.888036 


4.430167 


June 1953 


100 


2.942819 


4.528751 


July 1953 


100 


2.923373 


4.488341 


August 1953 . . 


80 


3.009451 


4.668415 


September 1953 


100 


3.204240 


5.059211 


October 1953 . 


100 


3.077283 


4.791176 


November 1953 


100 


3.069324 


4.750091 


December 1953 


62 


3.229206 


5.099838 


Total . 


911 


3.093213 


4.829690 


Ovigerous female: 








1952-53 


181 


3.011392 


4.656069 



o 



<2 40 



5 



. 




- x--x Ovigerous Females, N=181 


• 


' •— • Males & Nonovigerous 




Females. N = 911 , 




*/ 




// 




V 




1 




II 




1/ 




II 




1/ 




1/ 




1/ 




// 




// 




'/ 




// 




// 




// 




// 




sS 




^v / ^ 












. •> — -T i 1 1 1 1 1 1 1 L 


1— — 1 



TOTAL LENGTH (MM.) 
Figure 6. — Weight-length relation of commercial 
shrimp, M. vollenhovenii, for ovigerous females 
(range 47-131 mm., Log W = -4.656603 + 3.011392 
Log L) and males and nonovigerous females (range 
39-150 mm., Log W = -4.829560 + 3.092213 Log L) . 
Shrimp were captured in the lower St. Paul River, 
Liberia, 1952-53. 

and lengths for the ovigerous females and for 
the combined males and nonovigerous females. 
Ovigerous females were slightly heavier than 
males and nonovigerous females (fig. 6). 

Only a slight difference was seen between 
the weight-length relation of M. vollenhovenii 
and the weight-length data of pond-cultured 
M. rosenbergii given by Ling (1967a). The 
growth differential between the two species is 
exceedingly different — M. rosenbergii reached 
155 m. in 7 months. 



Fecundity and Spawning 

I estimated the fecundity by counting the 
number of eggs that displaced a known vol- 
ume of water. Because the fecundity of crus- 
taceans differs with size, the sample was se- 
lective in that small shrimp (76-82 mm.) and 
large shrimp (101-113 mm.) were used to es- 
timate numbers of eggs per female. In small 
shrimp 1,555 to 1,785 eggs displaced 0.1 ml. 
of water; in large shrimp 850 eggs displaced 
0.1 ml. of water. Estimates of the numbers of 
eggs carried externally by the small shrimp 



varied from 12,885 to 34,210 and by the large 
shrimp from 37,550 to 45,000. 

Ovigerous females were taken in the lower 
St. Paul River throughout the May-January 
fishery. The lengths of the ovigerous females 
ranged from 47 to 131 mm. and the mode was 
in the 80- to 90-mm. interval (fig. 7). Of the 
total number of ovigerous females, shrimp less 
than 60 mm. made up 2.5 percent, and shrimp 
greater than 115 mm. made up 2.7 percent of 
the catch. The higher percentage of females 
bearing advanced (brown and eyed) eggs oc- 
curred in the same months as the higher per- 
centages of females bearing less developed 
(red) eggs (table 6). This would indicate an 
embryonic period of less than 1 month. Ling 
(1967a) found the embryonic period in Macro- 
brachium rosenbergii was 19 to 20 days at 26 
to 28° C. 

Peak spawning periods occurred during the 
commercial seasons — in 1952, M. vollenhovenii 
spawned in August and December, and in 1953, 
in September and December (table 6). Raj- 
yalakshmi and Randhir (1967), reported that 
in India the commercial prawn, Macrobrachinm 
malcolmsonii (Edwards), has two spawning 
peaks. No explanation can be given for the 



20 -i 

15 

10- 



o 

<c 



41 



1952 SEASON 
N. 148 



Lx 



1953 SEASON 
N.336 



"H-i 



20 40 60 80 100 120 140 

TOTAL LENGTH [MM.) 

Figure 7. — Length distributions of ovigerous female 
shrimp, M. vollenhovenii, in the commercial catch, 
during the 1952-53 season, in the lower St. Paul 
River, -Liberia. 

smaller percentage of ovigerous females of 
M. vollenhovenii found in the 1952 catch than 
in that of 1953 (table 6). 

The zero age group was subjected to an 
intensive fishery soon after it appeared. 
Groups of 3 to 10 women drove large push-nets 
made of burlap sacking along the shore and 



Table 6. — Numbers and percentages of M. vollenhovenii females with eggs in the early (red) and late (brown) 
stages of development, and total number of ovigerous females during the 1952 and 1953 commercial seasons, 
in Liberia 



Month 



Shrimp 



Females with 
red eggs 



Females with 
brown eggs 



Total ovigerous 
females 



1952 season: 

July 

August . . . 
September 
October . . 
November 
December 
January . . 



Number 

388 
762 
312 
461 
545 
678 
69 



Total . . 

1953 season: 

May 

June 

July 

August . . 
September 
October . . 
November 
December 



3,215 



158 
839 
1,201 
86 
149 
630 
935 
874 



Number 

13 
35 

1 
12 

7 
17 





85 



4 
8 
47 
2 
22 
41 
35 
55 



Percent 

3.4 
4.6 
0.3 
2.6 
1.3 
2.5 
0.0 



2.6 



2.5 
1.0 
3.9 
2.3 
14.7 
6.5 
3.7 
6.3 



Number 

9 
27 

1 

3 

1 
20 

2 



63 



7 

1 
21 

4 
10 

8 
22 
49 



Percent 

2.3 
3.5 
0.3 
0.7 
0.2 
2.9 
2.9 



2.0 



4.4 
0.1 
1.7 
4.6 
6.7 
1.3 
2.4 
5.6 



Number 

22 
62 

2 
15 

8 
37 

2 



148 



11 

9 

68 

6 

32 

49 

57 

104 



Percent 

5.7 
8.1 
0.6 
3.3 
1.5 
5.4 
2.9 



4.6 



6.9 
1.1 
5.6 
6.9 

21.4 
7.8 
6.1 

11.9 



Total 4,872 



214 



4.4 



122 



2.5 



336 



6.9 



10 




incurs 



31 



• ' . iiiimiiiii 



Figure 8. — Lateral view of the commercial shrimp, M. vollenhovenii, with black-spot disease on the carapace, 

abdomen, and walking legs. 



caught countless numbers of young shrimp 
and larval fishes. The catch, molded into cakes 
and placed between banana leaves, was smoked 
and eaten by the fishermen. 

When I examined the catch made by the 
women on November 15, 1953, I found that the 
young shrimp averaged 5 to 10 mm. long. Be- 
fore November juvenile shrimp were not 
abundant, an indication that the group caught 
in November was from the peak spawning in 
September. The early development of M. vol- 
lenhovenii appears to be nearly identical to 
that of M. rosenbergii reported by Ling 
(1967a). Ling (1967a) found embryonic de- 
velopment was 19 to 20 days, larval develop- 
ment (planktonic) 30 to 45 days, or a total of 
50 to 65 days until the shrimp settled as 4.5- 
to 5.0-mm. juveniles. 

Disease 

A black-spot microbial infection was found 
around scratches on the body or legs of shrimp 
(fig. 8). Anderson and Conroy (1968) have 
reported similar diseases in Crustacea. The 
infection not only ate through the carapace 
or abdomen but also attacked underlying tis- 
sues such as the gill filaments or the abdominal 
muscles; the telson and walking legs also were 
heavily infected. At times, the infection 
formed a ring around the middle portion of a 



walking leg and caused part of the leg to fall 
off. Identification of the disease was not pos- 
sible because laboratory facilities were lacking. 
A sample of 150 shrimp examined on May 30, 
1953, had 137 infected. Though not confined 
to shrimp of any size range, the infection ap- 
peared to be most severe on large individuals. 
The palatability of the shrimp did not appear 
to be affected by the infection. A substantial 
mortality of M. vollenhovenii may occur at 
times from the disease. 

BIOLOGY OF M. macrobrachion 

The biology of M. macrobrachion, in this 
report, will include only a description of the 
small noncommercial species, and its contri- 
bution in numbers and size in the culls from 
the commercial catch. 

Description 

M. macrobrachion, a small species, is usually 
less than 75 mm. long. The body is a light 
blue-gray mottled with dark spots. The ros- 
trum is long and slender, and arches slightly 
upward at the tip; 8 to 10 dorsal spines extend 
from the carapace onto the rostrum, and a 
short space separates them from 2 spines at 
the tip of the rostrum; 4 to 6 spines are present 
on the ventral surface. The carpus of the 



11 



major chela is always as long or longer than 
the palm; the fingers are pubescent. The ex- 
ternal eggs of the female, in early stages of 
development, are green but turn to dark brown 
in the advanced, eyed stage. 

Species and Size Composition of 

Culls from the Commercial Catch 

I examined 221 shrimp 42 to 77 mm. long 
(discarded as too small to sell) on August 4, 
1952, for species and size composition (table 
7) . The bulk of the sample was M. macro- 
brachion (88 percent) while the commercial 
shrimp M. vollenhovenii made up the remain- 
ing portion (12 percent). Less than 5 percent 
of the specimens of M. vollenhovenii were under 
65 mm. long, whereas only 7 percent of the 
specimens of M. macrobrachion were larger 
than 65 mm. M. macrobrachion ovigerous fe- 
males were numerous and constituted 33 per- 
cent of the sample, which was a much higher 
percentage than that of M. vollenhovenii at 
0.5 percent. The ovigerous females of M. 
macrobrachion. were 46 to 61 mm. long, and 
59 percent of them were in the 50- to 54-mm. 
size interval. The nonovigerous females were 



42 to 72 mm. long; 29 percent were in the 
55- to 59-mm. size interval. The size range of 
M. macrobrachion in the sample was similar 
to that listed by Holthuis (1951) for specimens 
from Nigeria. 

Throughout the investigation, M. macro- 
brachion was predominant among culls from 
the commercial fishery. The commercial fish- 
ery harvested the adults of both species, with 
no apparent detriment to either species. 

ACKNOWLEDGMENTS 

My Liberian fishery aide, Momolu P. Mas- 
saquoi, gave me great assistance on this project. 
Ivan Pratt of the Oregon State University 
Zoology Department let me analyze the data 
and prepare this manuscript for a research 
course under his supervision. Cmdr. George 
E. Morris, U.S. Coast and Geodetic Survey, 
F.O.A., kindly supplied the salinity data for 
the Monrovia Freeport. Other persons who 
aided in the investigation were: President 
William Tubman, Secretary of Agriculture 
John Cooper, and A. Kini Freeman of Liberia; 
Fenner Chace and Horton H. Hobbs, Jr., U.S. 
National Museum; Stillman Wright and Elmer 



Table 7. — Length distribution and percentage of 221 shrimp, Macrobrachium vollenhovenii and M. macro- 
brachion, culled from the commercial catch in the lower St. Paul River, Liberia, August 4, 1952 



Species and 

total length 

(5-mm. intervals) 



Male and 
female, with- 
out eggs 



Females with 

green or red 

eggs 1 



Females with 
brown eggs 



Total ovigerous 
females 



Total shrimp 
examined 



No. 



% 



No. 



% 



No. 



% 



No. 



% 



M. 



Total 122 



55.1 



45 



20.3 



28 



12.6 



73 



32.3 



vollenhovenii: 

50-54 

55-59 

60-64 

65-69 

70-74 

75-79 



1 


0.4 


4 


1.8 


5 


2.3 


6 


2.7 


8 


3.6 


1 


0.4 



0.5 



0.5 



Total 25 



11.2 



0.5 



0.5 



No. 



195 



26 



% 



M. macrobrachion: 






















40-44 


2 


0.9 


— 


— 


— ■ 


— 


— 


— 


2 


0.9 


45-49 


12 


5.4 


7 


3.2 


2 


0.9 


9 


3.2 


21 


9.5 


50-54 


31 


14.0 


27 


12.2 


16 


7.2 


43 


19.5 


74 


33.5 


55-59 


35 


15.8 


10 


4.5 


10 


4.5 


20 


9.1 


55 


24.9 


60-64 


27 


12.2 


1 


0.4 


— 


— 


1 


0.5 


28 


12.7 


65-69 


10 


4.5 


— . 


— 


— 


— ■ 


— ■ 


— . 


10 


4.5 


70-74 


5 


2.3 


— 


— 


— 


— 


— 


— 


5 


2.3 



88.3 



1 


0.5 


4 


1.8 


5 


2.3 


6 


2.7 


8 


3.6 


2 


0.9 



11.8 



1 Eggs in early stages of development are green in M. macrobrachion and red in M. vollenhovenii, while eggs 
in advanced stages of both species are brown. 



12 



Higgins, U.S. Fish and Wildlife Service; Lyle 
Calvin, Leonard Coleman, and Laurie Leonard, 
Oregon State University; and Max Katz, Uni- 
versity of Washington. 



LITERATURE CITED 

ANDERSON, J. I. W., and D. A. CONROY. 

1968. The significance of disease in prelim- 
inary attempts to raise Crustacea in sea 
water. Proc. Ille Sympos. Comm. Off. 
Int. Epizoot. Etude Maladies Poissons, 
Separate 3, 8 pp. 
DOBKIN, S. 

1967. Abbreviated larval development in 
caridean shrimps and its significance in 
the artificial culture of these animals. 
FAO World Sci. Conf . on Biol, and Cult, 
of Shrimps and Prawns. Exp. Pap., 
Agenda item 8, FR: BCSP/67/E/53, 
12 pp. 
HERKLOTS, J. A. 

1857. Palaemon Vollenhovenii, nouvelle es- 
pe'ce de Crustace. Notices entomolo- 
giques. 2. Tijdschr. Ent. 1: 96-97. 
HOLTHUIS, LIPKE B. 

1951. The caridean Crustacea of tropical 
West Africa. Atlantide Rep. 2: 7-187. 
HOLTHUIS, L. B., and H. ROSA JR. 

1965. List of species of shrimps and prawns 
of economic value. FAO Fish. Tech. 
Pap. 52, 21 pp. 
LING, S. W. 

1967a. The general biology and develop- 
ment of Macrobrachium rosenbergii 
(de Man). FAO World Sci. Conf. on 
Biol, and Cult, of Shrimps and Prawns. 
Exp. Pap., Agenda item 3, FR: BCSP/ 
67/E/30, 18 pp. 

1967b. Methods of rearing and culturing 
Macrobrachium rosenbergii (de Man). 
FAO World Sci. Conf. on Biol, and Cult, 
of Shrimps and Prawns. Exp. Pap., 
Agenda item 8, FR: BCSP/67/E/31, 11 
pp. 
LING, S. W., and A. B. 0. MERICAN. 

1962. Notes on the life and habits of the 



adults and larval stages of Macrobrach- 
ium rosenbergii (De Man). Indo-Pac. 
Fish. Counc. Proc. 9th Sess., Sec. 2, 55- 
61. 

MAN, J. G. DE. 

1904. On some species of the genus Palae- 
mon Fabr., from Tahiti, Shanghai, New 
Guinea, and West Africa. Trans. Linn. 
Soc. Lond. Zool., Ser. 2, 9: 291-327. 

MILLER, GEORGE CARL. 

1960. The taxonomy and certain biological 
aspects of the crayfish of Oregon and 
Washington. M.S. thesis, Oreg. Sta. 
Univ., Cprvallis, Ore., 216 pp. 

MONOD, THEODORE. 

1966. Crevettes et crabes de la c6te occi- 
dentale dAfrique. Reunion de Special- 
istes C.S.A. sur les Crustaces, Zanzibar 
1964, Mem. Inst. Fond. Afr. Noire 77: 
103-234 (issued 1967). 

ORTON, CLAYTON R. 

1954. Agriculture of Liberia. U.S. For. 
Op. Adm., Dept. Agric, For. Agric. 
Serv., Ill pp. 

PRUTER, ALONZO T., and 

GEORGE Y. HARRY, JR. 
1952. Results of preliminary shrimp ex- 
ploration off the Oregon coast. Oreg. 
Fish. Comm., Res. Briefs 4(1): 12-24. 

RAJYALAKSHMI, T., and M. RANDHIR. 

1967. The commercial prawn Macrobrach- 
ium malcolmsonii (H. M. Edwards) of 
the river Godavary, a discussion on the 
trend and characteristics of the popu- 
lation during 1963-1966. FAO World 
Sci. Conf. on Cult, of Shrimps and 
Prawns, Mexico. Abstract, Agenda 
item 5, FR: BCSP/67/E/51. 

WILLIAMSON, D. I. 

1967. The type of development of prawns 
as a factor determining suitability for 
farming. FAO World Sci. Conf. on 
Biol, and Cult, of Shrimps and Prawns. 
Rev. Pap. Agenda item 8, FR: BCSP/ 
67/R/l, 6 pp. 

MS. #1926 
GPO 997-882 



13 



UNITED STATES 
DEPARTMENT OF COMMERCE 

NATIONAL OCEANIC & ATMOSPHERIC ADMINISTRATION 

NATIONAL MARINE FISHERIES SERVICE 

SCIENTIFIC PUBLICATIONS UNIT 

BLDG. 67, NAVAL SUPPORT ACTIVITY 

SEATTLE, WASHINGTON 98115 



OFFICIAL BUSINESS 



Return this sheet to above address, if you 
do NOT wish to receive this material Q, 
or if change of address is needed [] (indi- 
cate change and give ZIP Code). 




POSTAGE AND FEES PAID 
U.S. DEPARTMENT OF COMMI 



-